Radiolabeling of biomolecules, in particular peptides, and most particularly monoclonal or polyclonal antibodies, has been used as a means to track and detect the pathway or location of a particular peptide when administered to a patient or subject. Such radiolabelled peptides are capable of emitting low levels of gamma radiation, which can be detected and pin-pointed to a target organ or other substrate.
Radionuclides such as rhenium-186m and particularly, technetium-99m, are useful for biomolecule labeling since they are known to form relatively stable bonds with a sulfhydryl group thereof. However, for sulfhydryl group-bonding to occur, rhenium-186m and technetium-99m must be in the +3, +4 or +5 oxidation state. Because technetium-99m is most readily available as its pertechnetate-99m salt, i.e., a form of technetium having a +7 oxidation state, most technetium-99m species must be reduced prior to reaction with a sulfhydryl group.
The labeling of biomolecule sulfhydryl groups via reduction of pertechnetate-99m salt has been performed using stannous (Sn.sup.2+) ion as a reducing agent for technetium-99m. In particular, aqueous solutions of stannous ion formed from acidic solutions (D. W. Wong et al., Int. J. appl. Radiat. Isotopes, 29, 251 (1978); A. Schwarz et al., Abstract No. 695 from the "Proceedings of the 34th Annual Meeting," J. Nucl. Med., Vol. 28, No. 4, April 1987; B. A. Rhodes, Nucl. Med. Biol., 18(7), 667 (1991); G. L. Griffiths et al., Bioconjugate Chem., 3(2), 91 (1992); EP Patent Application 403 225 to Immunomedics, Inc.; U.S. Pat. No. 4,305,992 to Rhodes and U.S. Pat. No. 5,334,708 to Chang et al.); stannous ion in the presence of tartrate anion (B. A. Rhodes et al., J. Nucl. Med., 27(5), 685 (1986); G. L. Griffiths et al., Nucl. Med. Biol., 21(4), 649 (1994); U.S. Pat. No. 5,061,641 to Shocat et al.; U.S. Pat. No. 4,877,868 to Reno et al.; U.S. Pat. Nos. 5,346,687, 5,277,893, 5,102,990 and 5,078,985 to Rhodes; U.S. Pat. Nos. 4,424,200 and 4,323,546 to Crockford et al.; U.S. Pat. Nos. 4,472,371 and 4,311,688 to Burchiel et al.; U.S. Pat. No. 5,328,679 to Hansen et al.; and EP Patent Applications 419 203 and 336 678 to Immunomedics, Inc.); stannous ion in the presence of glucarate (K. Y. Pak et al., Abstract No. 268 from the "Proceedings of the 36th Annual Meeting," J. Nucl. Med., Vol. 30, No. 793 (1989); K. Y. Pak et al., J. Nucl. Med., 33, 144 (1992); A. F. Verbruggen, Eur. J. Nucl. Med., 17, 346 (1990)); stannous ion in the presence of benzoic acid derivatives (S. J. Mather et al., J. Nucl. Med., 31, 692 (1990); U.S. Pat. No. 4,666,698 to Schwarz; PCT Publication No. 85/03231 to Institutt for Energiteknikk; and U.S. Pat. No. 5,164,175 to Bremer); stannous ion in the presence of diethylenetriaminepentaacetic acid derivatives (U.S. Pat. Nos. 4,668,503 and 4,479,930 to Hnatowich; U.S. Pat. No. 4,652,440 to Paik et al.; and U.S. Pat. No. 4,421,735 to Haber et al.); stannous ion in the presence of saccharic acid (U.S. Pat. No. 5,317,091 to Subramanian; WO 88/07382 to Centocor Cardiovascular Imaging Partners, L.P.;) stannous ion in the presence of glucoheptonate (U.S. Pat. No. 4,670,545 to Fritzberg et al.); stannous ion in the presence of D-gluconate (U.S. Pat. No. 5,225,180 to Dean et al.) have been used to effect technetium-99m labeling of sulfhydryl group-bearing peptides. In addition, dithionite has been used as the reducing agent for pertechnetate-99m (U.S. Pat. No. 4,647,445 to Lees).
The labeling of sulfhydryl group-bearing peptides using .sup.99m TcNCl.sub.4.sup.- has also been described (WO 87/04164 to the University of Melbourne).
There are several drawbacks associated with the above-mentioned processes for labeling sulfhydryl group-bearing biomolecules. First, because hydrochloric acid solutions of stannous ions are generally employed as vehicles for the pertechnetate-99m salt reducing agent, and such solutions are generally admixed with solutions of the biomolecules to be labeled, the hydrochloric acid can denature or otherwise chemically modify the biomolecule to be labeled, potentially rendering it inactive. On the other hand, basic neutralization of the stannous ion/hydrochloric acid solution prior to admixing with the solution of the biomolecule to be labeled can be problematic if the biomolecule to be labeled is particularly sensitive to base and also because such neutralization adds an extra step to the labeling process. Thus, there is a need for a method for labeling biomolecules with a radionuclide, preferably with a pertechnetate-99m salt, that excludes the use of either acidic or basic solutions.
In addition, solutions of biomolecule to be labeled, radionuclide and radionuclide reducing agent that additionally contain additives such as tartrate ion, glucarate, benzoic acid derivatives, benzoic acid derivatives, diethylenetriaminepentaacetic acid derivatives, saccharic acid and D-gluconate can be expensive and/or time consuming to prepare. Thus, there is a need for a method of labeling biomolecules with a radionuclide, preferably with a pertechnetate-99m salt, that excludes the use of such additives.
Citation or identification of any reference in Section 2 of this application shall not be construed as an admission that such reference is available as prior art to the present invention.